1. Field of the Invention
This invention relates to a polyamide derived from toluenediamine and, more particularly, relates to a polyamide derived from toluenediamine and isophthalic acid, and optionally terephthalic acid, aliphatic diamine or a mixture thereof.
2. Description of Related Art
Plastics have been finding increased utility as replacements for metal in the manufacture of automobile body parts. Specifically, plastics have been incorporated in the production of vertical body panels and fenders. These plastics, however, have generally lacked the combined physical properties necessary to produce horizontal body panels paintable in conventional, high temperature, automotive paint bake ovens without substantial hand finishing steps. Problems arising in using these plastics as automotive reinforced horizontal body panels include the fact that either (a) the processing of these plastics is difficult because their melt viscosities are too high at processing temperatures below where substantial polymeric degradation occurs, (b) the polymers exhibit excessive shrinkage around reinforcing fibers upon cooling of the panel thereby causing a rough surface, (c) condensation reactions occur within the plastic upon exposure to heat during painting resulting in bubbling of the paint and distortion of the painted surface, or (d) the panels made from the plastic experience shape distortion at paint bake oven temperatures. Plastics for the production of horizontal automotive body panels should have the combined properties of (a) a high heat of distortion so that the shape of fiber reinforced parts made therefrom will not become distorted at the high temperatures encountered during painting, (b) a melt viscosity low enough at standard processing temperatures to permit processing thereof without substantial polymeric degradation, (c) an amorphous nature so that the plastic experiences minimum shrinkage around reinforcing fibers during cooling following painting thereof in a conventional, high temperature, automotive paint bake oven, (d) high resistance to standard automotive fluids, (e) low flammability, and (f) high flexural strength.
Thus, one object of the present invention is to provide a thermoplastic which is amorphous, has a high heat of distortion temperature, exhibits good chemical resistance, has a melt viscosity which is low enough at processing temperatures to permit processing without substantial polymeric degradation, has low flammability, and exhibits high strength.